An elevator assembly of a building can comprise a number of elevators. Each of the elevators normally comprises an elevator car and also an electric drive for moving the elevator car. The electric drive comprises a hoisting machine of the elevator and also a power supply apparatus, such as a frequency converter, of the hoisting machine. The elevator car is moved in the elevator hoistway e.g. with suspension ropes traveling via the traction sheave of the hoisting machine of the elevator.
The loading of an elevator assembly varies according to the operating situation. The elevator car and the counterweight are suspended on different sides of the traction sheave such that their weight difference produces a force difference acting on the traction sheave, which force difference in turn affects the magnitude of the torque needed from the elevator motor when driving the elevator. When the torque requirement of the elevator motor increases, the current of the elevator motor also increases. Simultaneously the number and load of the elevators in operation therefore affect e.g. the magnitude of the current needed from the electricity supply of the elevator assembly. On the other hand, an increase in the current of the elevator motor increases the loading exerted on the elevator motor and also on e.g. the frequency converter supplying power to the elevator motor. When the current increases the copper losses of the elevator motor increase; likewise, the current of the solid-state switches, such as IGBT transistors, of the frequency converter increases when the current of the elevator motor increases.
The aim is to increase the performance of an elevator assembly by increasing e.g. the speed and acceleration of the elevator car to as close as possible to the maximum possible value set by the dimensioning of the elevator assembly. Increasing the speed/acceleration of the elevator car, however, increases the loading exerted on the different parts of the elevator assembly. Attempts to improve the performance of an elevator assembly might result in service outages owing to overloading of the elevator assembly.
Experts subordinate to, and under the direction of, the applicant are thus continuously striving to develop control methods and operating methods of an elevator motor for improving the performance of an elevator assembly.